In view of the dangers associated with automobile travel, there is an ongoing need for enhanced automobile safety features. One possible area of increased automobile safety involves the vehicle's cruise control system. A cruise control system permits an operator to set a predetermined speed of travel and controls the vehicle to maintain the predetermined speed. However, as the vehicle approaches obstacles, such as other cars and pedestrians, driver attention and intervention are necessary to actuate the vehicle's brakes thus overriding the cruise control system and avoiding collisions.
To enhance the safety of cruise control systems, "intelligent" cruise control systems have been suggested. Intelligent cruise control systems typically include a detector for detecting obstacles in the path of the vehicle and a controller for actuating the vehicle's brakes and overriding the cruise control system in response to the detection of obstacles. Advantageously, intelligent cruise control systems can reduce the dependency on the driver for avoiding collisions.
Another possible area of increased automobile safety is in collision avoidance systems. Like intelligent cruise control systems, collision avoidance systems generally include a detector for detecting obstacles in the path of the vehicle and a controller for actuating the vehicle's brakes in response to detected obstacles in order to avoid collisions.
In both the intelligent cruise control and collision avoidance applications, it is necessary to provide a detector capable of accurately and reliability detecting objects in the path of the vehicle. Such a detector is sometimes referred to as a Forward Looking Sensor (FLS) and must be relatively insensitive to the relative location of the automobile and obstacles and environmental conditions, such as temperature, humidity, ice and rain.
Radar is a suitable technology for implementing an automotive FLS. One type of radar suitable for this purpose is Frequency Modulated Continuous Wave (FMCW) radar. In typical FMCW radar, the frequency of the transmitted CW signal linearly increases from a first predetermined frequency to a second predetermined frequency. FMCW radar has the advantages of high sensitivity, relatively low transmitter power and good range resolution.
Because the FLS is a consumer product which may affect the safety of vehicles, the accuracy and reliability of the sensor are tantamount. Aspects of the FLS which contribute to its accuracy and reliability include its susceptibility to noise and the overall precision with which received radio frequency (RF) signals are processed to detect objects within the field of view of the FLS. Susceptibility to noise for example can cause false detections and, even more deleteriously, cause an object to go undetected.
Further significant attributes of the FLS are related to its physical size and form factor. Preferably, the FLS is housed in a relatively small enclosure mountable behind the forward surface of the vehicle's engine housing, or grill. For accuracy and reliability, it is imperative that the transmit and receive antenna and circuitry are unaffected by attributes of the vehicle grill and are mounted to the vehicle in a predictable alignment.
Also impacting the accuracy and reliability of the FLS is the existence of foreign matter or objects which undesirably block one or more portions of the FLS transmit and/or receive antennas and in particular block portions of the RF energy propagating to and from the FLS transmit and receive antennas. Such blockage, can be caused by an accumulation, over a period of time, of foreign matter or objects in the region of the antenna aperture. Such foreign matter may be caused for example by environmental conditions such as temperature, humidity, ice, rain and the like. Such blockage can degrade, or in extreme cases even prevent, proper operation of the FLS. Once a vehicle in which an FLS is mounted is deployed on the road, a gradual, continual accumulation of foreign matter can occur. This results in a corresponding gradual decrease in FLS system performance thus making it relatively difficult to detect the existence of antenna blockage due to gradual accumulation of foreign matter.
It would, therefore, be desirable to provide an FLS which is capable of detecting antenna blockage. It would also be desirable to provide an FLS which is capable of detecting antenna blockage due to the accumulation of foreign matter, such as mud, ice, snow or the like, on the vehicle on that area of the vehicle in which the FLS is mounted. It would further be desirable to provide an FLS which detects antenna blockage and which alerts a system user of the existence of such blockage.